In solid ink imaging systems having intermediate members, ink is loaded into the system in a solid form, either as pellets or as ink sticks, and transported through a feed chute by a feed mechanism for delivery to a heater assembly. A heater plate in the heater assembly melts the solid ink impinging on the plate into a liquid that is delivered to a print head for jetting onto an intermediate member. In the print head, the liquid ink is typically maintained at a temperature that enables the ink to be ejected by the printing elements in the print head, but that preserves sufficient tackiness for the ink to adhere to the intermediate member. In some cases, however, the tackiness of the liquid ink may cause a portion of the ink to remain on the intermediate member after the image is transferred onto the media sheet. This remnant of the jetted image may later degrade other images formed on the intermediate member.
Solid ink jet imaging systems generally use an electronic form of an image to distribute ink melted from a solid ink stick or pellet in a manner that reproduces the electronic image. In some solid ink jet imaging systems, the electronic image may be used to control the ejection of ink directly onto a media sheet. In other solid ink jet imaging systems, the electronic image is used to eject ink onto an intermediate imaging member. A media sheet is then brought into contact with the intermediate imaging member in a nip formed between the intermediate member and a transfer roller. The heat and pressure in the nip helps transfer the ink image from the intermediate imaging member to the media sheet.
One issue arising from the transfer of an ink image from an intermediate imaging member to a media sheet is the transfer of some ink to other machine components. For example, ink may be transferred from the intermediate imaging member to a transfer roller when a media sheet is not correctly registered with the image being transferred to the media sheet. The pressure and heat in the nip may cause a portion of the ink to adhere to the transfer roller, at least temporarily. The ink on the transfer roller may eventually adhere to the back side of a subsequent media sheet. If duplex printing operations are being performed, the quality of the image on the back side is degraded by the ink that is an artifact from a previous processed image.
To address the accumulation of ink on a transfer roller, various release agent applicators have been designed. These release agent applicators provide a coating of a release agent, such as silicone oil, onto the transfer roller. The release agent coating helps reduce the likelihood of ink adhering to the transfer roller. The release agent applicator needs to be in fluid communication with a supply of release agent and the structure of the applicator needs to transport an effective amount of the release agent from the release agent supply to the transfer roller. An effective amount of release agent resists accumulation of ink on the transfer roller without providing excess release agent that is transferred to a media sheet. The transfer of release agent to a media sheet may also degrade image quality.
U.S. Pat. No. 6,434,357 describes various oil delivery systems for providing release agent to a transfer roller and some of the limitations encountered with these systems. In an effort to address some of these limitations, release agent rollers have been developed that use multiple layered materials about a roller to meter release agent to a transfer roller. For example, U.S. Pat. No. 6,212,355 describes a release agent roller that has an oil supply reservoir located along the central axis of the cylinder formed by the roller. The reservoir is perforated with pores that enable the oil to seep out of the reservoir. An oil distribution layer is wrapped around the reservoir to transport the oil seeping from the reservoir in an evenly distributed manner. An outer liquid permeation control layer encloses the oil distribution layer to regulate the release of the oil to the transfer roller. As explained above, regulation of the amount of the release agent is important to prevent excess oil from being applied to the transfer roller, and subsequently, to the media sheets.
In solid ink imaging systems having intermediate members, release agent is applied to the intermediate imaging member to reduce build-up of ink on the intermediate member. Release agent applicators for intermediate imaging members are required to provide release agent to the intermediate members at levels different than release agent applicators for transfer rollers. Specifically, release agent applicators for transfer rollers need to limit the amount of oil applied to the transfer roller because a portion of a transfer roller does come in contact with the media sheet passing through the transfer nip. Typically, release agent applied to a media sheet is 5 mg/sheet or less. In order to reduce the likelihood of liquid ink adhering to the intermediate imaging member, release agent is typically applied to an intermediate member at levels greater than 10 mg/sheet.
Application of release agent to an intermediate imaging member in the amounts noted above may be achieved with a sump system in which a roller is partially immersed in an oil sump. As the release agent roller of an image drum maintenance system rotates out of the sump, it applies release agent to the intermediate imaging member in an amount that is 10 mg/sheet or greater. Prior to the intermediate imaging member reaching the transfer roller nip, the release agent may be metered with a metering blade so the amount of oil on the intermediate member does not degrade the media sheet in the nip. The excess oil metered from the intermediate member is directed back into the sump.
While a release agent sump system provides release agent to the intermediate imaging member in an effective amount, it suffers from some limitations. One limitation arises from the use of a porous layer to apply release agent to the imaging member. The release agent is supplied to the porous layer from pores of a release agent reservoir. The porous layer absorbs enough release agent from the reservoir that it becomes saturated. This saturation prevents the porous layer from effectively picking up release agent that has been returned to the sump. Consequently, the release agent is lost as it languishes in the sump. Release agent continues to be supplied from the release agent reservoir, even though release agent is present in the sump, until the release agent reservoir is exhausted. Thus, the operational life of the image drum maintenance system is extinguished despite the presence of unused release agent.